This invention relates to circuit breakers of the molded case, narrow width type such as is shown and described in U.S. Pat. No. 3,081,386 to M. F. Koenig et al. dated Mar. 12, 1963 and owned by mesne assignments by the assignee herein. Circuit breakers of this type are normally utilized in residential and commercial applications up to 240 volts.
Circuit breakers and the panelboards or load-centers to which they mount are designed to be compact and physically compatible with existing apparatus. However, electrical utilities are providing increased available current in new installations. As a result, the short circuit interruption capacity requirement of circuit breakers has increased from 10,000 amps to 22,000 amps for new breaker designs, while existing apparatus designs place severe limitations on changes in physical arrangement and size.
One approach to achieving circuit protecting interruption of high short circuit currents has been to provide parallel, oppositely directed current paths in the circuit breaker, utilizing the blow-apart electromagnetic forces generated by such arrangement to rapidly open the contacts before harmful currents are let through the device into a protected circuit. The structural compactness of the circuit breaker and the location of its current carrying members can present a problem in providing parallel current paths of suitable length to make advantageous use of this electromagnetic force concept. Another problem associted with interruption of currents of the aforementioned magnitude in compact breakers is the extinguishing of the arc resulting from interruption of the circuit. It is important that the arc be extinguished quickly and positively to prevent harmful current from being carried by the arc to the protected circuit. The arc chamber and vent sizes and locations are established by designs of existing apparatus, and therefore must be made more effective within their existing parameters.